1. Field
This specification relates to a write strategy circuit, a write strategy method, and an optical disk apparatus using the write strategy circuit or the write strategy method. More particularly, this specification relates to a write strategy circuit, a write strategy method, and an optical disk apparatus for capturing data to be written to an optical disk.
2. Discussion of the Background
In a recorder for recording data on an optical disk having a pre-format such as CD-R/RW and DVD±RW/R, an LD (laser diode) driver irradiates a laser beam onto the optical disk according to serial data to be recorded, which has been generated by an optical disk encoder such as a CD or DVD encoder, and records the serial data on the optical disk. With the laser beam irradiation, a pit or mark having a length specified by the serial data based on a cycle unit of a predetermined channel clock signal is formed on a recording surface of the optical disk. Based on a difference in reflectivity between an irradiated portion where the pits or marks are formed and an un-irradiated portion on the recording surface of the optical disk, the recorded data can be read out from the optical disk.
The channel clock signal changes according to a recording speed of the optical disk. For example, the channel clock signal has a frequency of 4.32 MHz for a standard CD, and has a frequency of 26.16 MHz for a standard DVD. The marks or pits are formed on a spiral guide groove previously provided on the optical disk from the inner radius to the outer edge of the optical disk. Defining a unit cycle of the channel clock signal as T, the length of the mark is 3T to 11T in the case of CD, and 3T to 11T or 14T in the case of DVD.
The serial data generated by the optical disk encoder is an NRZ (Non-Return-to-Zero) signal, which changes based on the cycle unit of the channel clock signal. If a laser beam irradiates onto the optical disk according to the serial data, the pit or mark on the optical disk may be influenced by a thermal conduction, etc., such that the shape thereof may be skewed or may become nonuniform with the change in pit or mark length. In such a case, the data read out from the optical disk does not match with the data that has been recorded at the time of recording.
To prevent this, a correction is usually applied to the serial data, and a laser beam is irradiated according to the corrected signal. This correction is known as a write strategy. Applying an optimum write strategy according to a recording condition can improve a recording quality of an optical disk. Various standards of write strategy have been specified to record the optical disk of various types. Manufacturers of optical disk recorders or optical disk media, for example, develop products such as optical disk apparatuses in compliance with specific write strategy standards.
A write strategy correction is conventionally processed by the optical disk encoder. However, with higher recording speeds, a skew is caused between signals travelling along a long substrate wire provided between the optical disk encoder and the LD driver, thereby deteriorating a quality of data to be recorded. Therefore, it is more desirable to apply a write strategy in a vicinity of the LD driver for driving a semiconductor laser at the time of high-speed recording. In this case, the optical disk encoder supplies serial data and a channel clock signal to a write strategy circuit applying a write strategy correction. The write strategy circuit captures the serial data according to the received channel clock signal, measures the length of a series of pulses of the serial data, and applies a specific strategy correction to the serial data according to a waveform pattern of the pulses.
To achieve reliable data capturing, the phase of the channel clock signal and the phase of the serial data needs to be synchronized with each other. Generally, the phase of the channel clock signal and the phase of the serial data are slightly different due to an output delay difference of the optical disk encoder between the channel clock signal and the serial data, or a delay difference due to the difference in a substrate wire length between the channel clock signal and the serial data. Such a difference rarely affects the relationship between the phase of the channel clock signal and the phase of the serial data with slower optical disk recording speeds. However, with higher optical disk recording speeds, i.e., shorter channel clock signal cycles, this difference becomes more noticeable such that the edge of the channel clock signal and the edge of the serial data may not be optimally controlled, resulting in unreliable data capturing.
For example, FIG. 1 is a timing chart illustrating an operation of a background write strategy circuit. In FIG. 1, SD, CHCLK1, and SD1 correspond to input serial data input from the outside, a channel clock signal, and captured serial data captured by the write strategy circuit, respectively. As shown in FIG. 1, the rising edge of the channel clock signal CHCLK1 and the falling edge of the captured serial data SD1 coincide with each other. The captured serial data SD1 may have a data length ranging from 3 to 5 cycles of the channel clock signal CHCLK1, with respect to the input serial data SD having a data length of 4 cycles of the channel clock signal. Thus, the data to be read out may have a different length from the length of the data that has been recorded.